Separator

ABSTRACT

A separator and a method for separating putrescent solids from water in sewage. A vortex chamber (2) has an inlet (for the sewage), a first (solids) outlet (6) and a second (water) outlet (8). Near the outlet (6) there is a flow modifying member (14) which induces a secondary flow in the vortex chamber (2). A portion of this secondary flow passes radially inwardly beneath the member (14) and upwardly through a passage (18). The member (14), if suitably shaped and dimensioned, improves the efficiency of the separator.

FIELD OF THE INVENTION

This invention relates to a separator and a method of separating, and isparticularly, although not exclusively, concerned with the separation ofputrescent solid matter from water in sewerage systems.

BACKGROUND OF THE INVENTION

A sewer normally receives both storm water and domestic waste, thelatter containing putrescent matter. Before the sewage can bedischarged, for example into the sea, most of the putrescent matter mustbe removed, and this is conventionally done by screening and bysedimentation. However, the volume of sewage to be handled, particularlyunder storm conditions, places a heavy load on the conventionalseparation equipment, and it is desirable to effect at least apreliminary separation before the sewage reaches the conventionalseparation equipment.

BRIEF DESCRIPTION OF THE INVENTION

According to the present invention, there is provided a separatorcomprising:

a substantially closed vortex chamber having oppositely disposed ends;

a mixture inlet directed into the vortex chamber to promote a primary,circulating flow within the vortex chamber about a swirl axis extendingbetween the ends of the vortex chamber;

a first phase outlet disposed centrally at one of the ends of the vortexchamber;

a second phase outlet disposed in the region of the other end of thevortex chamber;

a flow modifying member provided within the vortex chamber adjacent thefirst phase outlet, the flow modifying member having a passage therein,the flow modifying member being adapted and positioned to induce asecondary flow within the vortex chamber, a portion of this secondaryflow passing radially inwardly, with respect to the swirl axis, betweenthe flow modifying member and the said one end of the vortex chamber andaway from the said one end through the passage.

In an embodiment of the present invention, the flow modifying member hasa conical outer surface, with a vortex angle of 60°.

When the separator is used to separate putrescent solids from sewage,the first phase outlet will be disposed at the bottom of the vortexchamber and will be the outlet for the putrescent solids, while thesecond phase outlet will be disposed at the top and will be the outletfor the clean water. There may be a trap for collecting floatable solidswhich would not be discharged through the first phase outlet.

There may be an annular dip plate extending into the vortex chamber,preferably from the top, in order to establish or stabilize a shear zonebetween a relatively fast outer circulating flow and a slower innerflow.

According to another aspect of the present invention, there is provideda method of separating two phases from a liquid mixture. The mixture isintroduced into a substantially closed vortex directed tangentially topromote a primary, circulating flow within the vortex chamber. A firstphase is removed through an outlet disposed centrally at one end of thevortex chamber while the second phase is removed through an outletdisposed at the other end of the vortex chamber. The flow in the vortexchamber is modified to induce a secondary flow therein by means of aflow modifying member adjacent the first phase outlet.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a section through a phase separator;

FIG. 2 illustrates an alternative construction for part of the separatorof FIG. 1;

FIG. 3 is a cross-section taken along the line III--III in FIG. 1; and

FIG. 4 is a top view of the separator of FIG. 1, with some parts removedfor clarity.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

The separator illustrated in the Figures comprises a cylindrical vortexchamber 2, having an inlet 4 and two outlets 6 and 8. The inlet 4 (seeparticularly FIG. 4), is directed somewhat tangentially so as to promotea circulating flow or swirl in the vortex chamber 2. This effect isenhanced by a deflector plate 10. The flow will circulate about a swirlaxis which can be considered to coincide with the central axis of thevortex chamber although fluctuating conditions will mean that this willnot always be the case.

The outlet 6 constitutes a solids outlet. As shown in FIG. 1, the bottomof the chamber 2 opens into a sump 12, which in turn discharges into theoutlet 6. There may be a shut-off valve in the outlet 6. Separatedsolids will be deposited in the sump 12 in the form of a sludge, and maybe discharged intermittently, for example into a mobile tanker. In caseswhere continuous solids discharge is possible, the sump 12 may bedispensed with, as shown in FIG. 2.

Above the outlet 6 there is a flow modifying member in the form of acone 14. The cone 14 is supported on the base of the vortex chamber 2 bysupport plates 16, the orientation of which is selected so as to directthe circulating flow inwardly towards the sump 12. There is an upwardlyextending passage 18 through the cone 14. The vertex angle of the cone14 is 60° in the embodiment illustrated, and its dimensions are suchthat the base of the cone terminates at a position approximately halfway between the central axis of the vortex chamber 2 and the outer wall.It must be appreciated, however, that the shape and dimensions of thecone 14, as well as those of other components of the separator, must bedetermined largely empirically for operation under given conditions,since it is very difficult to predict by theoretical means how thecomplex circulating flow of fluid in the separator will behave inpractice.

At the top of the vortex chamber 2, there is a baffle plate 20 supportedby plates 22 which act as flow spoilers for the clean water flowing tothe outlet 8. On its way to the outlet, the clean water passes throughan annular slot 21 defined between the baffle plate 20 and the top ofthe vortex chamber. This reduces the possibility of solid materialentering the clean water outlet 8, since such solid material will tendto accumulate near the swirl axis. The outlet 8 extends from an annularchamber 24, which may or may not be closed at the top. An aperture 26extends through the chamber 24 and the baffle plate 20 to provide accessfor a cleaning rod which can be passed through the passage 18 and thesump 12 to dislodge solid matter which may adhere to these parts.

At the top of the vortex chamber near the outer wall there is afloatable trap 28 and a floatables outlet 30. The floatables trap 28comprises a bottom wall 32 and an end wall 34, the construction beingsuch that any solid matter floating on the surface of the water in thevortex chamber is carried round into the trap 28, from where it may bedischarged through the outlet 30. In the present embodiment, as is clearfrom FIG. 4, the floatables trap is disposed opposite the outlet 8, andthe purpose of this is to reduce the possibility of floatable solidsbeing discharged through the clean water outlet 8. However, apart fromthis factor, the trap 28 could be disposed anywhere around thecircumference of the vortex chamber 2.

An annular dip plate 36 projects downwardly into the chamber 2 from thetop wall. As with the dimensions of the cone 14, the position and axialextent of the dip plate 36 must be determined empirically. Its functionis to create, or stabilize, a shear zone between an outer, fast-flowingflow and an inner, slower-flowing flow of the mixture in the vortexchamber.

In operation as part of a sewage system, and as an illustration of themethod of the present invention, sewage is passed into the vortexchamber 2 through the inlet 4. This creates a circulating flow in thechamber 2 which separates, with the assistance of the dip plate 36, intothe outer and inner flows mentioned above. The flow is such thatnon-floatable solid matter progresses down the lower wall 38 of thevortex chamber 2 and between the plates 16. Some solid matter will,however, be deposited on the outer surface of the cone 14, and the flowwill tend to move these deposits slowly up the cone 14. The cone 14 hasthe effect of creating a secondary flow up the outside of the cone,outwardly and down, a portion of the secondary flow passing beneath cone14 and circulating upwardly through the passage 18, and then outwardly.Deposits climbing up the outer wall of the cone 14 will eventually beentrained in this flow and so repeatedly pass between the plates 16 withsaid portion of the secondary flow until eventually they are depositedin the sump 12. At the upper end of the chamber, clean water passesthrough the slot 21 and between the plates 22 into the annular chamber24 and out of the outlet 8. Under some conditions, this water will beclean enough to pass directly to a tidal outfall. Any floatable solidswhich will not be passed to the outlet 6 will be caught in the trap 28and can then either be mixed with the solids issuing from the outlet 6or else disposed of separately.

The construction of the separator, and in particular the substantiallyclosed top, the annular outlet slot 21, and the cone 14, result in anefficient separation of the solids from the water with a relatively lowenergy consumption (i.e. requiring only a low pressure head at the inlet4). Although the invention has been described with primary reference tosewage, the principles can be applied to separation of other mixtures,for example solid/liquid, solid/gas, liquid/gas or liquid/liquid (suchas oil and water) mixtures. However in each case, the shape anddimensions of the various components must be determined empirically tosuit the prevailing conditions. By way of example, where oil and waterare to be separated and assuming the proportion of oil to water to besmall, the separator would operate best with the first phase outlet 6and the flow modifying member 14 at the top.

Under some circumstances, separation can be made more complete byinjecting gas such as air into the inlet 4, causing frothing of themixture with entrainment of solid particles in the froth.

I claim:
 1. A separator comprising:a substantially closed chamber havinga generally cylindrical outer wall and oppositely disposed end walls; amixture inlet directed into the chamber to promote within the chamber aprimary, circulating flow about a swirl axis extending between the endwalls and a secondary, toroidal flow coaxial with the swirl axis; afirst outlet disposed centrally in one of the end walls of the chamber;a second outlet disposed in the region of the other end wall of thechamber; and a flow modifying member provided within the chamberadjacent the first outlet and having a passage therein, the flowmodifying member defining with the said one end wall an annular slotwhich is disposed radially inwardly of the outer wall of the chamber,the flow modifying member being adapted and positioned to cause aportion of the secondary flow to pass radially inwardly, with respect tothe swirl axis, through the annular slot and away from the said one endwall through the passage in the flow modifying member.
 2. A separator asclaimed in claim 1, in which the flow modifying member has a conicalouter surface.
 3. A separator as claimed in claim 2, in which the vertexangle of the conical outer surface is 60°.
 4. A separator as claimed inclaim 2, in which the base of the cone terminates at a positionapproximately midway between the central axis of the chamber and theouter wall of the chamber.
 5. A separator as claimed in claim 4, furthercomprising support plates which support the flow modifying member on thesaid one end of the chamber, the support plates being oriented to directflow through the annular slot towards the first outlet.
 6. A separatoras claimed in claim 1, further comprising a baffle plate spaced from thesaid other end wall to define an annular slot centered on the swirlaxis, through which flow from the chamber passes to the second outlet.7. A separator as claimed in claim 1, further comprising a trap forcollecting floatable solids.
 8. A separator as claimed in claim 1,further comprising an annular dip plate extending into the chamber fromone end wall in order to establish or stabilize, in use, a shear zonebetween a relatively fast outer circulating flow and a slower innerflow.
 9. A separator as claimed in claim 1, in which the swirl axisextends upwardly.
 10. A separator as claimed in claim 9, in which thefirst outlet is at the bottom of the chamber and the second outlet is atthe top.
 11. A separator as claimed in claim 1, further comprising gasinjection means for injecting gas into the mixture inlet.